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PNP \ NPN Transistor doesnt do what it should do

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xReM1x

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hi, I built this simple circuit just for fun :
**broken link removed**
as you can see, it is basically a transistor switch that shoud open or close depends on the base current, the problem is, when I built this circuit, it works fine if the voltage to the led is less than ~1.5V (RED LED rated at 2.1V 20mA) but when the voltage is 2.1V its like there is capacitance at the gate, the led just doesnt flash to music like it is flashing in 1.5V or lower.
its like there is capacitance at the gate that changes with voltage. I also simulated the schematic and it works fine in ltspice.
I tried connecting it to my PC and to my phone, I tried 2 power supplys, tried also PNP and also NPN transistors, tried anything twice and the led doesnt work in it rated voltage.
anybody have any idea?
 

The Instructable was designed by a 10 years old kid who knows NOTHING about electronics:
1) It is missing a resistor in series with the LEDs to limit their current and the transistor's current so they do not blow up!
2) It is missing a resistor in series with the base of the transistor to limit the current so the transistor and/or music source do not blow up!
3) It is missing a diode to prevent emitter-base reverse voltage when the input signal swings negative from damaging the transistor.
4) It is missing an opamp to cancel the dead zone of about 0.7V before the transistor turns on.

By the way, a door opens and closes. A transistor turns on and turns off.
The transistor does not have a gate, instead it has a base.
 

The Instructable was designed by a 10 years old kid who knows NOTHING about electronics:
1) It is missing a resistor in series with the LEDs to limit their current and the transistor's current so they do not blow up!
2) It is missing a resistor in series with the base of the transistor to limit the current so the transistor and/or music source do not blow up!
3) It is missing a diode to prevent emitter-base reverse voltage when the input signal swings negative from damaging the transistor.
4) It is missing an opamp to cancel the dead zone of about 0.7V before the transistor turns on.

By the way, a door opens and closes. A transistor turns on and turns off.
The transistor does not have a gate, instead it has a base.

1.) yes, I added a resistor, I actually use 5V and a resistor
2.) also using 1K
3.) I dont use, should I?
4.) I also dont use, do I must? or else what will happend?

and yes my bad I meant base not a gate.
 

1. Each LED needs about 1.6V (for red, othe colors may need more) so with 4 in series you need at least 6.4V supply before there is any chance of them lighting up. I suggest 100 Ohms series resistor is also used to limit the current.
2. As the output impedance of your phone/PC is probably only a few Ohms, I suggest you use say 22 Ohms in the base.
3. It isn't essential but it is advisable, use a 1N4001 or equivalent with cathode end toward the transistor base pin.
4. Is the crux of the problem, the circuit is clearly designed by someone with almost no knowledge of electronics. It relies on the peaks of the audio waveform being able to drive the transistor into conduction, that means there has to be more than about 0.7V of audio (VERY loud in an earpiece!) before anything can happen. Voltages lower than that will not have any effect at all. With a suitable amplifier, rectifier and voltage offset you can make the LEDs start to light with a quiet sound and get progressively brighter as the volume increases. I guess that's what you really want.

Brian.
 

1. Each LED needs about 1.6V (for red, othe colors may need more) so with 4 in series you need at least 6.4V supply before there is any chance of them lighting up. I suggest 100 Ohms series resistor is also used to limit the current.
2. As the output impedance of your phone/PC is probably only a few Ohms, I suggest you use say 22 Ohms in the base.
3. It isn't essential but it is advisable, use a 1N4001 or equivalent with cathode end toward the transistor base pin.
4. Is the crux of the problem, the circuit is clearly designed by someone with almost no knowledge of electronics. It relies on the peaks of the audio waveform being able to drive the transistor into conduction, that means there has to be more than about 0.7V of audio (VERY loud in an earpiece!) before anything can happen. Voltages lower than that will not have any effect at all. With a suitable amplifier, rectifier and voltage offset you can make the LEDs start to light with a quiet sound and get progressively brighter as the volume increases. I guess that's what you really want.

Brian.
1. also my bad just for testing I use 1LED. before I used led strip 12V.
2. sure, will do!
3. First I will try without it just for testing.
4. well yes, I could also do it and thats what I planned for tomorrow, the thing is the my friend has built this schematic just with TIP31 NPN TRANSISTOR and a led strip and it works good for him. why the heck doesnt it works good for me?
 

The Instructable was designed to light up and blow up the LEDs and transistor when driven from the speaker output of a fairly high power amplifier. Then the 0.7V before the transistor conducts does not matter.
Here is a circuit that can be driven from your pc or phone that uses a little power amplifier to amplify music and drive many LEDs:
 

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  • LED flasher to music 3.png
    LED flasher to music 3.png
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The Instructable was designed to light up and blow up the LEDs and transistor when driven from the speaker output of a fairly high power amplifier. Then the 0.7V before the transistor conducts does not matter.
Here is a circuit that can be driven from your pc or phone that uses a little power amplifier to amplify music and drive many LEDs:
does it has to be LM386?
 
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The LM386 is very common in north America.
What other little power amplifier can you get that is still made?
 

The LM386 is very common in north America.
What other little power amplifier can you get that is still made?
well I wanted IC that I have in my parts box (common parts), I could get LM386 no problem just get the bus. but thats fine.
 

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